About the saliva test
Hampshire and Isle of Wight Saliva Testing Programme follows a successful pilot in Southampton, where students and staff in four local schools and the University of Southampton were tested on a weekly basis.
Read more about the success of the pilot programme.
How does the saliva test work?
The saliva test is very simple – all participants need to do is provide a small 2ml sample of saliva in a pot and return it to a drop-off point.
This is then transported to a laboratory, where it is tested for genetic material of the virus in saliva samples using a technique known as loop-mediated isothermal amplification (LAMP).
The result of the saliva test will tell participants whether or not they have an active COVID-19 infection at the actual time they took the test. This test does not tell participants whether they had the virus in the past, and a negative result does not protect them from catching it in the future.
As with all tests, people can test negative if they are in the early incubation phase of developing an infection, so may test positive at a later time.
What’s the difference between the saliva sample testing and swab testing?
The saliva test uses saliva provided in a small pot by participants. This is very simple and easy to do at home. The swab test requires a swab to be taken from the back of the throat and high up in the nose either by the participant or a healthcare professional.
The saliva test used in our programme and the swab test check samples for COVID-19 using different techniques.
Saliva samples are tested for the virus using a technique known as loop-mediated isothermal amplification (LAMP).
In the UK, swab samples are currently tested for the virus using different techniques called polymerase chain reaction (PCR) testing or lateral flow testing.
The LAMP technique can be conducted reliably, and more quickly than the PCR test, which is currently the standard reference test. In validation studies across multiple laboratories in the UK and in other countries, positive samples from LAMP tests have been ‘double tested’ against PCR tests and shown to be highly accurate.
What’s the difference between the saliva sample testing and lateral flow tests?
Lateral flow tests are used with swab samples and identify presence of the virus. The tests work in a similar way to a pregnancy test, giving a positive line if the virus is detected in the sample. One benefit of these tests is that results can be read in 10-30 minutes, but current evidence is that these tests have more ‘false positives’ and ‘false negatives’ than LAMP tests.
Is a saliva sample as good as a swab sample in picking up the active virus?
Yes. Evidence suggests that saliva samples are as good as swab samples. In addition, the saliva samples are very simple to provide repeatedly.
Is the saliva LAMP test accurate?
Saliva test samples analysed using the loop-mediated isothermal amplification (LAMP) technique have been ‘double tested’ against tests using the polymerase chain reaction (PCR) testing method.
LAMP has been shown to be highly accurate in detecting active infections– 100 per cent specific (the ability to correctly identify those without the virus) and over 95 per cent sensitive (the ability to correctly identify those with the virus). This means that false positives are extremely rare and false negatives can occur but are not common.
Could you get a different result from a saliva LAMP test and a swab PCR test on the same day?
We don’t recommend doing two tests on the same day but, if you do, a different result can occur but very rarely.
Test results can be affected by a variety of factors, including the testing technique used, the quality of the sample provided and when it was taken.
The saliva LAMP test and the PCR test look for different levels and different parts of genetic material of the virus within samples.
The LAMP test, for example, targets several independent regions of the virus, giving it very high specificity for the presence of intact virus, particularly in the days before symptoms of infection develop. High specificity means that false positive results are extremely rare. PCR tests are directed at a variety of different fragments of the virus.
There are two scenarios when a test on the same day using the two techniques might give a different result. Both would give a negative from saliva LAMP and a positive from swab PCR:
The first is where people who are recovering from a COVID-19 infection (with or without symptoms) may continue to have lingering fragments that can be picked up by the PCR test for many days after any symptoms commenced, without necessarily having intact virus that can be detected by LAMP testing.
The second is an uncommon scenario where a saliva LAMP test may be negative, even when the PCR test is truly positive and at a level suggesting active infection; this is a so-called false negative for the saliva test. If you have a positive result from a saliva LAMP test or a PCR test, you must follow government guidelines regarding self-isolation.
Can you get a different result from any other test?
No test is perfect. There is a possibility that a lateral flow test and saliva LAMP test result may give different results. This could be due to the manner in which the lateral flow test is conducted by the individual. The saliva LAMP test is a very reliable test which picks up more true positives and has fewer false positives than lateral flow tests.
What is a false negative?
A false negative result is when the test is reported as negative when the person really has an infectious virus present, which has not been picked up. This is not common with the saliva LAMP test.
What if I test negative on the saliva test and a few days later test positive?
A negative saliva LAMP test tells you that at the time of sample collection there was no detectable infectious virus particle in the saliva. However, if the test is taken during the incubation period in the early days after a person has been infected, the number of virus particles may not yet be at a detectable level, and so a person could go on to test positive on a subsequent day.
To date, evidence from our and other testing studies is that the rate of false negative saliva LAMP tests is low for active infections and very similar to that of the reference swab PCR tests.
It is also possible to test negative one day and positive some days later if a new infection is acquired after the negative test. Find out more about what to do if you test positive.
What is a false positive?
A false positive is where the test result is positive but there is no infectious virus present. We have tested many thousands of samples within this Programme and have had no false positive results - so you can be confident, if you test positive and you/your household need to isolate, it is because you have the virus.
Will my saliva sample be used for anything else?
Your saliva sample will only be tested for COVID-19. Tests are being conducted at a testing site with full accreditation and no DNA will be extracted or stored.
Can I use a saliva test if I have symptoms?
No. This is because our programme is only for testing people who are asymptomatic (people without any COVID-19 symptoms), as we don’t have access to enough tests to use them for people who have symptoms.
If you have symptoms, you should order a test via the NHS national testing programme that has been set up for this purpose. The national testing programme will offer you either a postal test kit, or an appointment at a site for testing.
Why is asymptomatic testing important?
Testing people without symptoms of COVID-19 is important as it can identify those who may be spreading the virus but aren’t aware of it. Many people with COVID-19 don’t have symptoms but can still transmit the virus, and those who do develop symptoms can be infectious for a few days beforehand.
Once someone knows that they have the virus, they, their household and close contacts must follow government advice around self-isolation, reducing the chance of it being spread to their family and friends, as well as anyone else they may come into contact with.
Asymptomatic testing within schools, colleges and universities can help us to continue to offer education in COVID-secure environments.
Should I continue taking regular tests if I am isolating?
If you are isolating due to a positive test result or because you are a contact of someone who has tested positive, you should not continue testing. Please complete your full isolation period. A negative test would not shorten your isolation period. Once you are no longer isolating, continue testing regularly as you did before.
If you are based in a school and have been asked to take regular tests instead of self-isolating as a contact, please follow the instructions you have been given.
If you are based at university and have been asked to isolate until you have had two negative tests, then please follow the instructions provided by the university.
How does virus infection work?
Viruses consist of a relatively short length of genetic material which is surrounded by a protein coat. They cannot replicate by themselves; they need a host cell. In the case of COVID-19, these include the cells in our salivary glands in the mouth and the respiratory system.
The virus particles enter the host cell and release their genetic material. The host cell then replicates this genetic material thousands of times and creates new virus particles. This can destroy the host cell and many of the new virus particles are released to then infect other cells.
In the meantime, your immune system cells detect the COVID-19 and start producing antibodies to destroy the virus. This can take time and you may feel ill and display symptoms whilst this is happening. Alternatively, you may have no discernible symptoms at all.
The average time between exposure to the virus and symptoms developing is estimated as five days, and for most people it is four-six days. For some people this time may be as short as two days or as long as 14 days. Importantly, many people may have active virus in their saliva and other secretions before they develop symptoms, and could therefore transmit infection to others, such as in the droplets that we all produce when talking.
A negative saliva test result means you did not have detectable the virus when you spat in your pot, but it may be early in the incubation period OR you may have picked it up since your test!
Sam has unknowingly acquired the virus from a contact on Wednesday. He does his routine saliva test at 9am on Friday morning. He gets a negative saliva test message on Friday evening. He develops a fever and cough on the following Monday and gets an NHS swab test which comes back positive.
Tina does a saliva test at 9am on Friday morning. Tina meets her friends on Friday and sits chatting with them indoors. Whilst there, she is exposed to COVID-19 by breathing in the virus particles. Tina gets a negative saliva test text message on Friday evening, but the virus particles are now replicating in her respiratory system cells. By Sunday, Tina has a fever and cough and gets an NHS swab test which comes back positive.
When should I resume saliva LAMP testing after a positive test result?
For Saliva LAMP testing you should start testing again once your period of self-isolation following the positive test has ended. The rules for self-isolation following a positive test are as follows:
- If you have symptoms – self-isolate for 10 days from when your symptoms started.
- If you have not had symptoms – self-isolate for 10 days from when you had the test.
- If you get symptoms while you're self-isolating - the 10 days restarts from when your symptoms started.
Should I continue with the testing programme if I've had the vaccination?
Yes, please keep testing as planned. No vaccine is completely effective and so it is still possible for you to get infected and pass the virus on to others.
Will the fact that I've had a vaccination affect my test result?
No, the vaccine will not affect your test result. The vaccine itself won't cause you to test positive. The test picks up infections, not your response to the vaccine.