Scrapping Covid surveillance study would put public health at risk | Letter

For any monitoring system to be reliable and cost-effective, it cannot rely solely on self-reported tests, writes Prof Sylvia Richardson of the Royal Statistical Society

Sajid Javid is right to argue against scrapping the Office for National Statistics' Covid surveillance study (Cabinet splits emerge over living with Covid' strategy and free testing, 17 February). Throughout the pandemic, national surveillance studies have provided invaluable information to support decision-making.

For any real-time health surveillance system to be reliable and cost-effective, it cannot rely solely on self-reported tests. These data sets are likely to be biased, as it is impossible to know how many people are also reporting their negative results and, if tests start to come with a cost, how many people simply aren't testing. If we are to get reliable information about the prevalence of Covid, it is essential to maintain studies such as the ONS's and React to allow statisticians to estimate infectiousness and the proportion of the population who are infected (including those without symptoms), as well as to identify new variants.