Applied Epi Community

Estimate level of inmunity to SARS-CoV2


I have been asked to estimate the level of immunity to SARS-CoV2 in my country. What are the ways in which I can do this and what should I take into consideration?

Thank you for your help


It sounds like you are being asked to measure the prevalence of antibodies for SARS-CoV2. Without going into the laboratory based details on how you can do this and what biological samples you will have to collect, lets think about it from an epidemiological methods approach. In order to measure prevalence, you will need to conduct a survey of some type. The type of survey you conduct, the sample size you include, how you select the participants in your survey will all impact on the logistics, cost and feasibility of doing such a survey.

Using blood donors

The easiest approach would be to do a survey in blood donors. This avoids you having to take new biological samples from participants and generally all donated blood is easily accessible in a single location. The aspects to consider for this approach are: 1) how representative of the general population are your blood donors? If only young, healthy women donate blood, then their antibodies for SARS-CoV2 will not reflect the immunity in the overall population. 2) Did the blood donors when they donated blood consent to their blood being screened for all diseases? 3) If you identify SARS-CoV2 antibodies in blood donations, are you obliged to inform the individual that donated the blood of their status and do you have the resources to do this?

Using another target group of participants

You could also consider to target other participants that might be easier to find than conducting a survey in the general population. These might include healthworkers (who are likely to have higher immunity compared to the general population due to their exposure to Covid patients), students in universities (not representative of the whole population as they are young and have different exposures), students in primary schools (would provide a valuable estimate for this age group, but unlikely to be representative of the general population), etc.

Doing a population based survey

Conducting a population based survey would likely be the most representative, but also the most complicated and costly to implement. You can however ensure you sample a representative proportion of the population (by age and sex) and thus calculate seroprevalence for SARS-CoV2 antibodies that actually represent the most likely epidemiological profile for this disease in your country at that moment in time.

Hope this helps


Thank you for your complete answer