Thread by @DrZoeHyde

(1/9) Study of #COVID19 in schools in New South Wales from 25 January to 10 April.

In the setting of low community transmission, few cases generally occurred (except for an outbreak in a childcare centre). There are some big limitations though. Read on...
thelancet.com/journals/lanch…

(2/9) During the study, 27 primary cases (12 in children and 15 in adults) were detected in 15 schools and 10 childcare centres.

Detected secondary cases were:

➡️ 5 cases (3 children and 2 adults) in 3 schools;
➡️ 13 cases (6 adults and 7 children) in 1 childcare centre.

(3/9) At first glance, this seems reassuring but only 44% of close contacts were tested.

The authors write: "the majority of close contacts were tested after developing symptoms, so infected contacts with no or mild symptoms might have been missed."

(4/9) It is also likely that not all close contacts were identified, because cases were only considered infectious for up to 24 hours before symptom onset. Cases may actually be infectious before that.

(5/9) The authors write: "It is probable that additional close contacts would have been identified in our study had the 48-h presymptomatic contact definition been operational before the commencement of our study."

(6/9) Additionally, the median time that primary cases were at school while infectious was only 2 days.

This suggests that cases were detected quickly and had limited opportunity to transmit the virus to others.

(7/9) But the largest issue is that schools switched to distance learning for almost all students during the study (on 23 March). Childcare centres remained open.

School attendance was only 5% after this point.

Almost all cases occurred before the switch to distance learning.

(8/9) Finally, community transmission was low at the time of the study.

The majority (58%) of #COVID19 cases in New South Wales were acquired overseas, and the virus was largely circulating among the contacts of returned travellers at this point.

(9/9) In conclusion, the study suggests that #COVID19 outbreaks are not common in schools when community transmission is low.

However, the extent of transmission may have been underestimated because not all contacts were tested. Interpret these findings carefully.